when you write,
y(n+1)=x(n)+0.005.*(((y).^2)+(7*y)+2)/(3*x((y).^2)+((1-x)*(3*((y)^2)+7)));
^
you're trying to access the zeroth element of x (since y is vector with all zeroes except its first element). You need to rewrite that equation. How does the equation in your book look like?
Anyway, if you want to create a vector with 0.005 increaments use linspace or colon(:) operator.
